Klum gave birth Wednesday to Johan Riley Fyodor Taiwo Samuel, who weighed 8 pounds, 11 ounces, according to Seal's Web site. It did not say where the baby was born.
"He is healthy, beautiful and looks just like his mother," the posting read.
The couple, married in May 2005, have a 1-year-old son, Henry Guenther Ademola Dashtu Samuel.
Klum also has a daughter, Leni, from a previous relationship with Formula One manager Flavio Briatore.
The 33-year-old German supermodel, host of Bravo's "Project Runway," and the Grammy-winning singer, 43, began dating in February 2004.